'dotnet watch' crashes while being modified by CoPilot

### Describe the bug

While prompting in CoPilot Opus prompt in Rider in parallel with running in dotnet watch, it crashed in watching file content:

```
❌ An unexpected error occurred: System.InvalidOperationException: Unexpected true - file HotReloadMSBuildWorkspace.cs line 158
at Microsoft.CodeAnalysis.Contract.Fail(String message, Int32 lineNumber, String filePath)
at Microsoft.CodeAnalysis.ExternalAccess.HotReload.Api.HotReloadMSBuildWorkspace.UpdateFileContentAsync(IEnumerable`1 changedFiles, CancellationToken cancellationToken)
at Microsoft.DotNet.Watch.CompilationHandler.UpdateFileContentAsync(IReadOnlyList`1 changedFiles, CancellationToken cancellationToken)
at Microsoft.DotNet.Watch.HotReloadDotNetWatcher.<>c__DisplayClass13_3.<g__CaptureChangedFilesSnapshot|8>d.MoveNext()
--- End of stack trace from previous location ---
at Microsoft.DotNet.Watch.HotReloadDotNetWatcher.WatchAsync(CancellationToken shutdownCancellationToken)
at Microsoft.DotNet.Watch.HotReloadDotNetWatcher.WatchAsync(CancellationToken shutdownCancellationToken)
at Microsoft.DotNet.Watch.Program.RunAsync()

```

The launch profile used is:
```
"Highlight Watch": {
"commandName": "Executable",
"executablePath": "dotnet",
"launchBrowser": true,
"launchUrl": "https://localhost:5001/",
"hotReloadEnabled": false,
"workingDirectory": "$(ProjectDir)",
"hotReloadProfile": "blazorwasm",
"commandLineArgs": "watch run --no-launch-profile",
"environmentVariables": {
"ASPNETCORE_ENVIRONMENT": "Development",
"ASPNETCORE_URLS": "https://localhost:5001;http://localhost:5000"
}
},
```

### Steps to reproduce

Run watch while prompting in CoPilot :-)

### Expected behavior

Watch should not crash

### Actual behavior

Watch crashes

### Is this a regression?

_No response_

### Are there any workarounds?

_No response_

### dotnet --info output

```console

```

### IDE version

_No response_

### Other details

_No response_

Start with the HotReloadMSBuildWorkspace.UpdateFileContentAsync stack frame at HotReloadMSBuildWorkspace.cs line 158 and the dotnet watch path through CompilationHandler and HotReloadDotNetWatcher. Reproduce the crash using the provided launch profile while prompting in Copilot from Rider, and capture the missing dotnet --info details. Done means dotnet watch no longer crashes during this file-change scenario.

Written by the indexing model from the issue text.